BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to a process for the separation of carbon monoxide
from a fluid containing carbon monoxide and nitrogen by means of a zeolitic molecular
sieve agglomerate comprising a bonded product of a crystalline zeolite and a binder.
2. Description of Related Art
[0002] It is well known in the art that natural or synthetic zeolites are industrially utilized
for drying, purification, recovery, and/or separation of various fluids such as hydrocarbon
streams and atmospheric air employing the adsorptive properties of the components
in the fluids on the zeolites. The effectiveness of the treatments of a fluid stream
such as drying, purification, recovery and/or separation depends upon the type of
zeolite to be used as well as the components of a fluid to be treated. For example,
Na-A zeolite (or sodium cation form type-A crystalline zeolite) pellets comprising
crystalline zeolite Na-A and a clay mineral as main constituents can adsorb molecules
having size and shape to permit entrance through a micro-pore of 3.8 angstroms such
as water vapor, hydrogen sulphide, carbon dioxide, ethane, ethyl alcohol and butadiene,
while other molecules such as propane, cyclic hydrocarbons and compressor oil being
excluded. The Na-A zeolite pellets, therefore, have been advantageously utilized as
an adsorbent for such as natural gas and solvent drying, carbon dioxide removal from
natural gas streams. Furthermore, Na-X zeolite pellets comprising crystals of Na-X
zeolite having rational formula of:
Na₈₆[(AlO₂ ₈₆(SiO₂)₁₀₆]·276 H₂O
and a clay mineral as main constituents can adsorb molecules smaller than an effective
diameter of 10 angstroms such as iso-paraffins, iso-olefins and di-n-butylamine and
exclude molecules having a large diameter of more than 10 angstroms such as tri-n-butylamine,
and have been employed for the purposes of for example, simultaneous removal of moisture
and carbon dioxide from fluid streams containing the same or the removal of sulphur
compounds from hydrocarbon streams containing the same.
[0003] It is also known in the art that the entire or partial exchange of the cation in
a crystalline zeolite to another has a marked effect on its adsorptivity and cation-exchanged
forms of Na-form zeolites such as calcium- and potassium-forms are used depending
upon services therewith. Barium-exchanged form zeolites, however, have not been of
wide prevalence in industrial services, although some of the said forms have been
proposed. For example, barium form zeolite X prepared by exchanging 90% or more of
sodium cations in the above-mentioned zeolite Na-X with barium cations is described
in, for example, U.S. Patent No. 2,882,244. The Ba-form zeolite X exhibits the desirable
separation property for various sorbates such as nitrogen and oxygen. However, the
desirable separation property of the conventional barium-form zeolite X is susceptible
to be impaired during processing, i.e., the blending of the barium-form zeolite and
the binder, the fashioning of the mixture into suitable forms and the firing of the
formed material at elevated temperatures has prevented the prevalence thereof in the
practical use.
[0004] One the other hand, although the above-mentioned Na-X zeolite has been employed for
the above-mentioned purpose, for example, as an industrial adsorbent for separation
and/or removal, it is still not satisfactory for some uses as an adsorbent, for example,
the separation of carbon monoxide and nitrogen and the separation of oxygen and nitrogen
of atmospheric air.
[0005] EP-A-0109063 discloses faujasite-containing compositions having an Si/Al ratio of
1 to 2. These compositions may be used for the separation of nitrogen from nitrogen-containing
gas. Furthermore, it is disclosed that the faujasite used may be ion-exchanged with
Mg, Ca, Sr, Ba and mixtures thereof.
[0006] US-A-2882244 discloses the production of an adsorbent of the molecular sieve type.
Particularly the preparation of zeolite X is disclosed, wherein the electrovalence
of the aluminium-containing tetrahedra in the crystal may be balanced by a cation,
such as from Ca²⁺, Sr²⁺, Ba²⁺, Na⁺ and K⁺.
[0007] US-A-3140932 relates to the separation of an oxygen/nitrogen mixture and to a process
for separating such mixture by contact with cation exchanged forms of crystalline
zeolites.
SUMMARY OF THE INVENTION
[0008] Accordingly, the object of the present invention is to eliminate the above-mentioned
disadvantages of the processes using conventional Na-X zeolite and to provide a process
for separating carbon monoxide from a fluid containing carbon monoxide and nitrogen.
In accordance with the present invention a process for separating carbon monoxide
from a fluid containing carbon monoxide and nitrogen is provided, which comprises
treating the fluid with a zeolitic molecular sieve agglomerate comprising a bonded
product of a crystalline zeolite and a binder, said crystalline zeolite having, except
from water of crystallisation, the formula:
Ba
43xNa
86(1-x)[(AlO₂)₈₆(SiO₂)₁₀₆] (I)
wherein x is a number from 0.6 to 0.8.
[0009] In a preferred embodiment the present invention provides a process, wherein the weight
ratio of the crystalline zeolite of the above formula (I) to the binder is 70:30 to
90:10.
In another preferred embodiment the crystalline zeolite has, except for water of crystallisation,
the above mentioned formula (I), wherein x is a number from 0.62 to 0.78.
In yet another preferred embodiment the agglomerate comprises particles having a size
of 60 to 80 meshes.
In still another preferred embodiment of the process of the present invention the
carbon monoxide/nitrogen separation coefficient is in the range of about 3.75 to about
3.90.
In another preferred embodiment of the present invention the nitrogen retention time
is about 0.10 and the carbon monoxide retention time is about 3.86.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present invention will be better understood from the following descriptions presented
in connection with the accompanying drawings, in which:
Fig. 1 is an X-ray diffraction pattern of the barium-exchanged crystalline zeolite
X obtained in Example 1;
Fig. 2 is an X-ray diffraction pattern of the barium-exchanged crystalline zeolite
X obtained in Example 2;
Fig. 3 is an X-ray diffraction pattern of the barium-exchanged crystalline zeolite
X obtained in Example 3;
Fig. 4 is an X-ray diffraction pattern of the barium-exchanged crystalline zeolite
X obtained in Example 4;
Fig. 5 is an X-ray diffraction pattern of the Na-X zeolite powder used as the starting
material in Examples 1 to 4;
Fig. 6 is a chromatogram obtained in Example 10;
Fig. 7 is a chromatogram obtained in Comparative Example 4;
Fig. 8 is a chromatogram obtained in Example 11; and
Fig. 9 is a chromatogram obtained in Comparative Example 5.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0011] As mentioned above, the crystalline zeolites used in the process of the present invention
are those having, except for the water of crystallization, the general formula (I)
and obtained by substituting barium cation for 60% to 80% of the sodium cation of
the Na-X zeolite. When the barium cation exchange ratio is less than 60%, the separation
property of the sorbates in a fluid stream containing the same is not improved, when
the agglomerates prepared by blending the zeolite and a clay binder and activated
at elevated temperatures are compared with the conventional Na-X zeolite agglomerates
prepared by the same procedure as the above-mentioned Ba-X zeolite agglomerates. Contrary
to this, the Ba-X having higher than 80% of cation exchange ratio causes a difficulty
in crystalline stability thereof, when manufactured into agglomerates for the industrial
use with maintaining the desired adsorptive and/or separation property.
[0012] The Na-X zeolite used as a starting material in the preparation of the barium-exchanged
crystalline zeolite X according to the present invention is known and commercially
available, which can also be prepared by the methods disclosed in, for example, U.S.
Patent No. 2,882, 244 and 2,979,381.
[0013] The partial barium ion exchange of the Na-X zeolite can be carried out by, for example,
a method disclosed in U.S. Patent No. 2,882,244. For example, the Na-X zeolite is
treated with a solution containing a certain amount of barium cation, such as an aqueous
or alcoholic solution containing a certain amount of a barium compound to obtain the
desired barium-exchanged crystalline zeolite X. A 0.1 to 1 mole/liter solution of
barium chloride or barium nitrate can be typically employed in the preparation of
the desired barium-exchanged crystalline zeolite X. The desired barium ion exchange
ratio of 60% to 80% can be easily achieved by controlling the relative amounts of
the barium compound and the Na-X zeolite used in the treatment process.
[0014] The barium-exchanged crystalline zeolite having the above-mentioned general formula
(I) thus prepared can be advantageously converted into a zeolitic molecular sieve
agglomerate in any conventional manner, for example, by blending the binders, fashioning
the mixture into suitable forms and activating at elevated temperatures. Thus, the
clay is dried to give a bonded product and the water of hydration of the zeolite is
lost. The binders usable in the present invention include any conventional binders,
for example, bentonite clays such as bentonite, kaolin clays such as kaolin, plastic
ball clays, and clays of attapulgite.
[0015] Although there is no specific limitations in the mixing ratio of the crystalline
zeolite and the binder, the preferable weight ratio of the crystalline zeolite to
the binder is 70:30 to 90:10. The barium-exchanged crystalline zeolite X and the binder
and, optionally, some conventional additives, can be mixed together by using any conventional
mechanical means such as a muller, kneader, or blender. The mixture is then formed
in any conventional manner, for example, by using an extruder, pelletizer, or any
other bead-forming means to pellets or other suitable forms. The resultant agglomerates
are finally dried and calcined at elevated temperatures (e.g., 150°C to 300°C and
550°C to 700°C, respectively). Thus, the desired zeolitic molecular sieve agglomerate
can be obtained. The water of crystallization (i.e., 276 molecule of water pre unit
cell) contained in the crystal of the starting Na-X zeolite or the barium-exchanged
product thereof is substantially removed to zero during the drying and calcining steps.
Thus, the desired molecular sieve agglomerate suitable for use in the drying, adsorption,
separation, or removal of a certain gas or other components can be produced.
[0016] The molecular sieve agglomerate including the barium-exchanged type crystalline zeolite,
in which 60% to 80% of the sodium ions is exchanged with barium ions, can be manufactured
by preparing a zeolitic molecular sieve agglomerate including Na-X zeolite and the
above-mentioned binder, followed by partially exchanging the sodium ions of the resultant
Na-X zeolite agglomerate with barium ions. The Na-X zeolitic molecular sieve agglomerate
can be prepared in any conventional manner, e.g., by mixing the Na-X zeolite with
the binder, followed by drying and calcining the formed mixture at elevated temperatures
(e.g., 150°C to 300°C and 550°C to 700°C, respectively). The resultant Na-X zeolitic
molecular sieve agglomerate can be treated with the above-mentioned solution containing
barium ions. The resultant barium-exchanged molecular sieve agglomerate is then dried
and activated at a temperature of, for example, 200°C to 550°C.
[0017] The molecular sieve agglomerates including, as a main constituent, the barium-exchanged
crystalline zeolite having the above-mentioned general formula (I) have excellent
thermal stability and thermal deterioration resistance and can be effectively used
in the separation and purification of gas mixtures. Especially, the present molecular
sieve agglomerates can be advantageously used in the separation of carbon monoxide
and nitrogen, in the separation of nitrogen and oxygen, or in the removal of water
vapor and carbon dioxide from air containing the same.
[0018] The present invention now will be further illustrated by, but is by no means limited
to, the following Examples.
Example 1
[0019] A 100 g amount (dry weight) of Na-X zeolite powder available from UNION SHOWA K.K.
was saturated with moisutre in ambient conditions. Then, the Na-X zeolite powder was
slurried by adding 250 ml of water. An aqueous solution of 50 g of BaCl₂·2H₂O having
a purity of 98.5% in 250 ml of water was added to the above prepared slurry. The mixture
was then allowed to stand, while occasionally stirring, at room temperature for one
night.
[0020] The crystal thus obtained was filtered and thoroughly washed with water until no
chlorine ions were detected in the washed liquor. After air dried, the crystalline
zeolite was heated at a temperature of 200°C for 2 hours and, then at a temperature
of 450°C for 2 hours. Thus, the crystalline zeolite was activated.
[0021] The zeolite crystal thus prepared had a barium content of 21.85% by weight determined
by gravimetric analysis and a sodium content of 4.47% by weight determined by atomic-absorption
spectroscopic analysis. The barium ion exchange ratio calculated from these analysis
data was 62%.
[0022] The X-ray diffraction pattern of the barium-exchanged crystalline zeolite obtained
above was as shown in Fig. 1. The lattice spacings calculated from each peak of Fig.
1 were fundamentally consistent with those of Ba-X disclosed in U.S. Patent No. 2,882,244,
except that there were strong peaks at α = 7.57 Å and 3.83 Å, which are strongly observed
in the case of Na-X. For comparison, the X-ray diffraction pattern of the starting
molecular sieve 13X powder in Fig. 5. The reason why the peak height of the X-ray
diffraction pattern in Fig. 1 is lower than that of the molecular sieve 13X powder
is that the X-ray absorption coefficient of barium is large.
[0023] It is clear from the above data that the sodium ions of the starting Na-X zeolite
were partially exchanged with barium ions.
[0024] The water absorption capacity of the barium-exchanged crystalline zeolite obtained
above was 27.3 g/100 g, as determined under the conditions of 17.5 mmHg and 25°C in
a McBain Bakr apparatus. Although this water adsorption capacity was lower than that
of the starting Na-X zeolite powder (i.e., 33.3 g/100 g), this was caused by the fact
that the specific gravity of the crystalline zeolite was increased and that the internal
void volume of the crystals per unit cell was changed due to the exchange of sodium
ion with the barium ion. When the adsorption capacity was compared in terms of the
adsorption amount per unit cell, there was no substantial difference between the water
adsorption capacities.
Example 2
[0025] Barium-exchanged crystalline zeolite was prepared in the same manner as in Example
1, except that 60 g of BaCl₂·2H₂O was used.
[0026] The barium content and the sodium content of the resultant crystalline zeolite determined
in the same manner as in Example 1 were 22.79% by weight and 4.04% by weight, respectively.
The barium ion exchange ratio obtained from these data was 65%. The X-ray diffraction
pattern of the crystalline zeolite obtained above was as shown in Fig. 2.
[0027] The water absorption capacity of the crystalline zeolite was 26.9 g/100 g as determined
in the same manner as in Example 1.
Example 3
[0028] Barium-exchanged crystalline zeolite was prepared in the same manner as in Example
1, except that 80 g of BaCl₂·2H₂O was used.
[0029] The barium content and the sodium content of the resultant crystalline determined
in the same manner as in Example 1 were 25.92% by weight and 2.89% by weight, respectively.
The barium ion exchange ratio obtained from these data was 75%. The X-ray diffraction
pattern of the crystalline zeolite obtained above was as shown in Fig. 3.
[0030] The water adsorption capacity of the crystalline zeolite was 26.6 g/100 g as determined
in the same manner as in Example 1.
Example 4
[0031] Barium-exchanged crystalline zeolite was prepared in the same manner as in Example
3, except that the mixture was heated at a temperature of 80°C for 1 hour after adding
the barium solution, instead of being allowed to stand for one night.
[0032] The barium content and the sodium content of the resultant crystalline zeolite determined
in the same manner as in Example 1 were 25.62% by weight and 2.95% by weight, respectively.
The barium ion exchange ratio obtained from these data was 74%. The X-ray diffraction
pattern of the crystalline zeolite obtained above was as shown in Fig. 4.
[0033] The water adsorption capacity of the crystalline zeolite was 26.5 g/100 g as determined
in the same manner as Example 1.
Example 5
[0034] A 8 kg amount of barium-exchanged crystalline zeolite X having a barium ion exchange
ratio of 66% prepared in the same manner as in Example 2 was saturated with moisture
in ambient conditions. The crystalline zeolite thus obtained was mixed with 2 kg of
attapulgite by adding 2.7 kg of water. The resultant mixture was extruded through
a die and broken into pellets having a diameter of 1.6 mm.
[0035] The pellets obtained above were heated at a temperature of 200°C for 2 hours and
were, then, calcined at a temperature of 650°C for 2 hours for the activation. The
pellets thus obtained were crushed to the particles having a size of 60 to 80 meshes
in terms of Tyler mesh. The CO/N₂ separation capacity of the resultant agglomerate
particles was determined by gas chromatography. That is, the separation coefficient
defined by a ratio of the retention times of CO/N₂ was 3.90, when
1 ml of a gas mixture (CO/N₂=1/2 by volume) was passed through a gas chromatograph column
packed with the above-prepared agglomerate particles under the conditions of a column
temperature of 40°C and a feed rate of 30 ml/min with a helium carrier gas and a thermal
conductivity detector (TCD). The column diameter was 3 mm and the packed height was
0.5 m.
[0036] Furthermore, the water adsorption capacity and the CO₂ adsorption capacity of the
agglomerate particles determined in the same manner as in Example 1 were 23.6 g/100
g and 17.0 g/100 g, respectively.
Example 6
[0037] A 8 kg amount of barium-exchanged crystalline zeolite having a barium ion exchange
ratio of 77% prepared in the same manner as in Example 3 was agglomerated in the same
manner as in Example 5. Thus, the agglomerate particles having a size of 60 to 80
meshes were obtained.
[0038] The CO/N₂ separation coefficient of the resultant agglomerate particles, determined
in the same manner as in Example 5, was 3.75. The water adsorption capacity and the
CO₂ adsorption capacity of the agglomerate particles, determined in the same manner
as in Example 1, were 22.5 g/100 g and 15.9 g/100 g, respectively.
Comparative Example 1
[0039] Barium-exchanged crystalline zeolite was prepared in the same manner as in Example
1, except that 25 g of BaCl₂·2H₂O was used.
[0040] The barium content and the sodium content of the resultant crystalline zeolite determined
in the same manner as in Example 1 were 14.7% by weight and 6.2% by weight, respectively.
The barium ion exchange ratio obtained from these data was 44%.
[0041] The agglomerates of the barium-exchanged Na-X zeolite were prepared in the same manner
as in Example 5.
[0042] The CO/N₂ separation coefficient of the resultant agglomerate particles, determined
in the same manner as in Example 5 was 3.53. The water adsorption capacity and the
CO₂ adsorption capacity of the agglomerate particles, determined in the same manner
as in Example 1, were 24.7 g/100 g and 16.9 g/100 g, respectively.
Comparative Example 2
[0043] Barium-exchanged crystalline zeolite was prepared in the same manner as in Example
1, except that 200 g of BaCl₂·2H₂O was used.
[0044] The barium content and the sodium content of the resultant crystalline zeolite determined
in the same manner as in Example 1 were 27.9% by weight and 0.7% by weight, respectively.
The barium ion exchange ratio obtained from these data was 93%.
[0045] The water absorption capacity of the crystalline zeolite was 21.5 g/100 g as determined
in the same manner as in Example 1.
Example 7
[0046] A 2 kg amount of Na-X zeolite in the form of pellets having a diameter of 1.6 mm
(available from UNION SHOWA K.K.) was saturated with moisture in ambient conditions.
Then, the hydrated pellets were dipped in a solution of 1 kg of BaCl₂·2H₂O dissolved
in 10 liters of water and were allowed to stand, with occasionally stirring, at room
temperature for one night.
[0047] The pellets thus obtained was filtered and thoroughly washed with water until no
chlorine ions were detected in the washed liquor. After air dried, the pellets were
heated at a temperature of 200°C for 2 hours and, then at a temperature of 450°C for
2 hours. Thus, the
[0048] pellets were activated. The barium content and the sodium content of the resultant
pellets determined in the same manner as in Example 1 were 18.8% by weight and 3.6%
by weight, respectively. The barium ion exchange ratio obtained from these data was
64%.
[0049] The CO/N₂ separation coefficient of the resultant pellets, determined in the same
manner as in Example 5, was 3.86. The water adsorption capacity and the CO₂ adsorption
capacity of the pellets, determined in the same manner as in Example 1, were 22.7
g/100 g and 15.9 g/100 g, respectively.
Example 8
[0050] A 1.8 kg amount of the barium-exchanged crystalline zeolite agglomerate particles
prepared in Example 6 above was packed into a adsorption column having a nominal diameter
of 50 mm and a length of 1100 mm. A gas mixture of air, water vapor, and carbon dioxide
(CO₂ = 340 to 440 ppm by volume, H₂O = saturated at 25°C, and 5 kg/cm²G) was passed
through the column at a flow rate of 3.8 Nm³/hr.
[0051] As a result, the CO₂ adsorption capacity at the CO₂ stoichiometric point was 2.84
g/100 g of zeolite and the mass transfer zone was 23.0% of the total amount of the
packed zeolite particles. No breakthrough of the water vapor was observed during the
test operation.
Example 9
[0052] The adsorption test was carried out in the same manner as in Example 8, except that
the agglomerate pellets obtained in Example 7 were used.
[0053] The CO₂ adsorption capacity at the CO₂ stoichiometric point was 2.8 g/100 g of the
zeolite and the mass transfer zone was 23.3% of the total amount of the packed zeolite
pellets. No. breakthrough of the water vapor was observed during the test operation.
Comparative Example 3
[0054] The adsorption test was carried out in the same manner as in Example 8, except that
Na-X zeolite commercially available from UNION SHOWA K.K. were used.
[0055] The CO₂ adsorption capacity at the CO₂ stoichiometric point was 2.5 g/100 g of the
zeolite and the mass transfer zone was 28% of the total amount of the packed zeolite
pellets. No breakthrough of the water vapor was observed during the test operation.
Example 10
[0056] The barium-exchanged molecular sieve 13X pellets having a barium exchange ratio of
78% obtained in the same manner as in Example 7, were packed into a gas chromatography
column having a nominal diameter of 3 mm. The packed height was 500 mm.
[0057] A gas mixture of carbon monoxide and nitrogen (i.e., CO/N₂ = 1/2 by volume) was passed
through the column under a pressure of 0.6 to 0.7 kg/cm²G. The resultant chromatogram
was as shown in Fig. 6.
Comparative Example 4
[0058] The separation test of carbon monoxide and nitrogen was carried out in the same manner
as in Example 10, except that the commercially available Na-X zeolite was packed in
the column.
[0059] The resultant chromatogram was shown in Fig. 7.
Example 11
[0060] The separation test of nitrogen and oxygen from air was carried out in the same manner
as in Example 10, except that the zeolite particles X having a barium exchange ratio
of 65% and air were used as the adsorbent and the gas mixture, respectively.
[0061] The resultant chromatogram was as shown in Fig. 8.
Comparative Example 5
[0062] The separation test of Comparative Example 4 was repeated, except that the air was
used as a gas mixture.
[0063] The resultant chromatogram was as shown in Fig. 9.